Angioplasty catheters are widely used for removing plaque from arteries. Some "roto-rooter" angioplasty catheters have rotary blades, which cut away the excess plaque. These catheters may cause damage to the coronary arteries.
An impact lithotripsy catheter is described in U.S. Pat. No. 5,246,447, issued Sep. 21, 1993 in the name of Rosen et al. This catheter includes a mass cap, supported by the windings of helically wound guide, at the distal end of the catheter. Laser pulses are applied through an optical fiber extending axially through the body of the catheter, to vaporize a portion of the mass cap at each pulse. The vaporization, in turn, results in rapid expansion of material at the proximal end of the mass cap, which generates a high velocity, short forward impulse. The impulse is transmitted through the mass cap to the kidney stone or other hard deposit. While effective in fragmenting calciferous and other hard deposits, this type of catheter may not remove soft or fatty deposits.
Acoustic catheters are used for angioplasty, for ablating plaque by sonification of the fluid in the affected artery. Some acoustic ablative catheters have a metal wire extending through the body of the catheter, and have an acoustic generator external to the body, and coupled to the proximal end of the metal wire. These catheters suffer from the problem of standing waves along the length of the wire, and of heating at nodes of the standing wave pattern. This type of acoustic ablation catheter has relatively low efficiency in coupling energy from the acoustic generator to the ablation site, because of heating losses at the nodes of the standing wave. Consequently, it is necessary to apply considerable acoustic power to the proximal end of the catheter, in order to couple enough energy to the catheter to effectively ablate plaque at the proximal end in the presence of the losses. The heating losses at the nodes, with this large acoustic input power, may cause damage to the patient at the locations of the nodes.
U.S. Pat. No. 5,423,797, issued Jun. 13, 1995 in the name of Adrian et al. describes an ablation catheter which includes a rotary-to-axial motion converter at its distal end, driven by a rotating shaft. The motion converter converts the rotary motion of the shaft into axially-directed acoustic pulsations, which are coupled to the surrounding fluid to thereby generate the acoustic energy by which ablation is accomplished. In one embodiment described therein, the motion converter includes an uneven or wavy surface (swash plate) which is rotated by the shaft, and a follower which is free for axial motion, which bears against the wavy surface, and is pushed distally by the protruding portions of the surface. While effective at generating acoustic energy, this type of catheter involves the use of moving parts.
Improved acoustic catheters are desired.